Mechanisms Of Resistance And Sublethal Effects Of Methoxyfenozide In Cotton Bollworm, Helicoverpa Armigera

In pest control and management, the impact to survive insect in the aspects of physiological andbiological characteristics called the sublethal effects. In the laboratory methoxyfenozide-resistant strain（R） and susceptible strains（S） of the cotton bollworm was cultivated. To investigate the sublethal effects，the biochemical resistance mechanism and resistance target molecular mechanism, we studiedmethoxyfenozide-resistant strain （R） and susceptible strains（S） of the cotton bollworm in the laboratory.A methoxyfenozide-resistant strain（R,18.5-fold resistance） of cotton bollworm （CBW）, Helicoverpaarmigera （Hübner） and the homologous control strain （S） were used to evaluate sublethal effects ofmethoxyfenozide on the insect. The results indicated that the sublethal dose delayed the CBW growth andprolonged the pupa period and reduced pupation rate, emergence rate and hatching rate in both of the twostrains, especially in the S. After treatment，growth inhibition of S and R is37.3%and21.2%, average ofpupal weight decreased for0.037g and0.063g. There is abnormality in different growing periods,especially abnormal rate of moth increasing to20%. In addtion, effect of reproduction in S is muchlarger. Average of fecundity is only352and hatching rate of eggs is55%.The3rd instar larvae of resistant strain （R,28-fold resistance） and homologous susceptible strain（S）were treated with LC₄₀of methoxyfenozide for48h, and then the specific activities of mixed functionoxidases （MFO）, general esterases （EST） and glutathione S-transferase （GSTs） in3rd,4th,5th and6thinstar larvae were measured. For S strains,the activities of EST increased at3rd,5th and6th instars,especially in3rd instar, activities of GSTs significantly increased only in5th instar, activity of MFOdecreased in6th instar. For R strains, activities of EST obviously decreased in3rd and6th instars, bothactivities of GST and MFO significantly decreased in all tested instars. Under non-insecticide treatment,Compared with S strains, activities of GSTs of the R strains increased in3rd⁶th instars, Whereas theEST and the MFO increased only in the3rd instar in5th instar respectively. The result of synergiststreatment showed that synergism ratio of DEM,PBO,DEF is4.32,0.86,1.67. As a result, the resistance tomethoxyfenozide is closed related with increasing activities of GSTs in cotton bollworm. EST and GSTsmay be induced by LC₄₀dose of methoxyfenozide in S strains，but activities of the three enzymes wereinhibited in R strains.In order to explore the biochemical mechanisms of the cotton bollworm （CBW）, Helicoverpaarmigera （Hübner）, resistance to methoxyfenozide, activity of protective enzymes includingcatalase（CAT）, peroxidase（POD） and superoxide（SOD）, and phenoloxidase（PO） were tested in resistantstrain（R,28-fold resistance） of cotton bollworm, and the homologous susceptible strain （S）. There wereno significant differences in CAT, POD and PO activities between the S and R, but SOD activity of the Rincreased obviously. The result shows that actitvity of SOD in S is about twice the large of that in R.The ultraspiracle protein（USP）gene, part of the20E binding proteins in cotton bollworm, wascloned from the S and R strains. The full-length cDNA of USP gene contains2262bp.The ORF showsthat USP contains1245bp and will be translated into a Peptide which contains414amino acids. USP protein genes from the R and S strains were cloned and sequenced, separately,4mutation sites weredetected from the R resistant strain. However, the translated amino acids were found2mutation sites.The result indicates that the mutation sites did not affect function of E structural domain.